Experimental and numerical investigation of the effect of diffusive air injection on turbulence generation and flashback propensity in swirl combustors

Combustion instabilities are considered one of the most serious challenges for developing combustion systems through the years. Undesirable issues linked to these phenomena represent a risk for such systems especially in gas turbines and propulsion devices where the propagation of these instabilities can even lead to considerable damages. Flame flashback from the combustion chamber into premixer represents one of the most important combustion instability issue in swirl combustors used in gas turbines. This study proposes an experimental and numerical approach to validate the use of a central air injection in swirl combustors to reduce flame flashback propensity via controlling the turbulence generation at the tip of the flame while pushing the CRZ, thus retarding the appearance of the CIVB, to mitigate the progression of combustion into the system. Results showed the potential of this technique to affect turbulence generation and pushing back the flame into the combustion chamber, increasing operability limits. Very good agreement was achieved between experimental and numerical results, demonstrating that the use of injection through the central core of the system not only controls the position of the recirculation zone but also affects turbulence and mitigates other forms of flame flashback.